Cascading Ice–Rock Avalanche Multi-Hazard Early Warning in the Bhote Koshi–Trishuli River Corridor

Cascading hazards in high-mountain environments can evolve rapidly from slope failure to destructive downstream flooding, challenging conventional early-warning systems. The 26 August 2026 Langtang Lirung rock–ice avalanche and subsequent flood cascade along the Bhote Koshi–Trishuli corridor were examined through a retrospective synthesis of seismic, terrain, hydrological and documentary evidence. Event chronology reconstruction and reach-based analysis yielded apparent celerities of 47.3, 20.9 and 6.0 m s−1 across successive reaches of 22, 44 and 130 km. Propagation over the approximately 196 km corridor occurred within 6 h 43 min of the catalogued seismic marker. Deterministic sensitivity analysis preserved the downstream decline in celerity under the specified timing and distance perturbations, although uncertainty in event initiation, flow formation and observational timing limits hydraulic interpretation. The warning-chain assessment identified insufficient evidence to verify end-to-end operational capability. A two-stage framework is proposed, which combines evidence-based hazard screening, operational readiness, scenario development and direct emergency escalation.